Communication devices such as terminals or wireless devices are also known as e.g. User Equipments (UEs), mobile terminals, wireless terminals and/or mobile stations.
Such terminals are enabled to communicate wirelessly in a wireless communication system or a cellular communications network, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications network.
The above terminals or wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, or tablets with wireless capability, just to mention some further examples. The terminals or wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. an “eNB”, an “eNodeB”, a “NodeB”, a B node”, or a Base Transceiver Station (BTS), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated at the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals or wireless devices within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
A Universal Mobile Telecommunications System (UMTS) is a third generation (3G) telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS Terrestrial Radio Access Network (UTRAN) is essentially a RAN using Wideband Code Division Multiple Access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipment. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a Radio Network Controller (RNC) or a Base Station Controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs and BSCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3GPP and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface.
In the 3GPP LTE, base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
The 3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
Multi-antenna techniques may significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a Multiple-Input Multiple-Output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO systems.
In a 3GPP LTE communications network, a Radio Link Control (RLC) protocol, such as the RLC protocol according to section 5.1.3.2 “Receive operations” of the 3GPP TS 36.322 standard, always performs reordering to guarantee in-sequence order delivery of data units to a Packet Data Convergence Protocol (PDCP) and further on from there. Thus, the reordering functionality is performed to reorder data units received out of order to guarantee that the received data units are delivered in a correct order. The RLC is a layer 2 protocol used by LTE on the air interface. Further, the RLC is located on top of the 3GPP MAC layer and below the PDCP layer. The PDCP layer is a data link layer or a data forwarding layer. The PDCP protocol in LTE, e.g. the PDCP protocol according to section 5.1.2.1.4 “Procedures for DRBs mapped on RLC AM and for LWA bearers when the reordering function is use” of the 3GPP TS 36.323 standard, does also have a function to perform reordering of its Protocol Data Units (PDUs), which is used at times when the RLC does not manage to guarantee in-sequence delivery, e.g. during times when the RLC is re-established, e.g. for handover etc., and when data is sent using two parallel RLC protocols and different physical layer adaptation functions. This is sometimes referred to as dual connectivity.
The 3GPP New Radio (NR) communications network, e.g. the 5G communications network, aims at providing larger bandwidths at higher frequencies with more challenging radio coverage, and is expected to have an increased dependency on PDCP anchored dual connectivity and/or multi-connectivity.
As a result, it is agreed to require from the PDCP to always provide the reordering function, i.e. not only at times when lower layers are re-established or configured for dual connectivity. The complexity of the RLC is decreased such that it does not need to perform reordering but may deliver without delay directly after Service Data Unit (SDU) assembly. An SDU is a unit of data that has been passed down from an upper layer to a lower layer. The SDU has not yet been encapsulated into a Protocol Data Unit (PDU) by the lower layer. In other words, the SDU of the lower layer is the input to the protocol of the lower layer and the PDU of the lower layer is the output from the protocol of the lower layer. Thus, the input to a protocol of a layer may be referred to as the SDU and the output of the protocol of the layer may be referred to as the PDU. Further, the SDU at any given layer (n) is the PDU of the layer above (n+1). In effect the SDU is the payload of a given PDU. The layer (n−1) adds headers or footers, or both, to the SDU when forming the PDU. In this disclosure the terms the RLC SDU and the PDCP PDU are interpreted as being equal and used interchangeably. It follows that the PDCP will meet new challenges to continuously execute reordering, at least at occasions when in sequence delivery to one or more layers above the PDCP is needed. The layer above the PDCP layer may be a data link layer, a network layer, a transport layer, a session layer, a presentation layer or an application layer just to give some examples.
The reordering function in the LTE PDCP is using a t-Reordering timer to limit the time to wait for missing PDCP PDUs. If one or more out-of-sequence PDCP PDUs are received by the PDCP layer, from lower layers, e.g. from the RLC layer, i.e. there is one or more missing PDCP PDUs, the reordering function in LTE PDCP will do the following:                1. The one or more out-of-sequence PDCP PDUs are buffered and not immediately forwarded.        2. The t-Reordering timer is started. Note that if t-Reordering timer is already running, it shall neither be started again nor additionally be started for each of the one or more missing PDUs, i.e. only one t-Reordering timer is running per PDCP entity at any given time. The PDCP entity may be some piece of software running a separate instance of a full PDCP protocol between a network node, such as an eNB or a gNB, and a network node, such as UE, for a specific, so called, radio bearer. There are different bearers in LTE, signalling radio bearers aka SRB and data radio bearers aka DRB. There is one entity for each such bearer, thus also a timer for each such bearer.        3. If more PDCP PDUs, e.g. some of the one or more missing PDCP PDUs, are received out-of-sequence before t-Reordering expire, they are buffered and not immediately forwarded to an upper layer.        4. If the one or more missing PDCP PDUs are all received before the t-Reordering timer expire, they are immediately forwarded in-sequence to the upper layer, followed by an in-sequence delivery of buffered PDUs to the upper layer.        5. But if instead the t-Reordering timer expires before the one or more missing PDUs are all received, there is no more waiting but instead only the buffered PDCP PDUs will be forwarded to upper layers. If by any chance any of the one or more missing PDCP PDUs is received after the t-Reordering timer has expired, it will arrive too late and will be discarded.        6. The lower end of the reception window will be advanced to match the latest PDCP PDU that has been forwarded to upper layers.        
The PDCP reordering functionality provides a robust way to ensure in-order delivery for PDCP PDUs that are received within a certain time period, but at the cost of setting a limit for how late PDUs, e.g. packets, may arrive.
EP 3 063 909 A1 relates to techniques for aggregating data from a wireless wide area network (WWAN) and wireless local area network (WLAN). In some aspects, a packet convergence entity (e.g., PDCP layer entity) communicates with first and second radio access technology (RAT) links. The packet convergence entity may determine from which of the first and second RAT links a data packet is received and may monitor a sequence number value of each of the received data packets. The packet convergence entity may perform one or more actions based on a determination that the data packets are received out of order. For example, the packet convergence entity may deliver the data packets to an upper layer entity as they are received (e.g., in order or out of order), may reorder the data packets and ignore data packet losses, and/or may request retransmissions of missing data packets